The infrared spectrum of He–HCO+

The vibrational predissociation spectrum of the He–HCO+ proton bound complex has been recorded in the 3 μm (C–H stretch) region by monitoring the HCO+ photofragment current. A rotationally resolved, parallel band is observed, red shifted 12.4 cm−1 from the ν1 transition of free HCO+. Analysis in terms of a diatomiclike Hamiltonian yields B″=0.2900±0.0002 cm−1, D″=(1.00±0.06)×10−5 cm−1, B′=0.2898±0.0010 cm−1, and ν1=3076.313±0.010 cm−1. Localized perturbations to ν1 rotational levels are observed and are tentatively ascribed to interactions with combination vibrational states made up of quanta of the CO stretch and HCO+ bend, and those of the low frequency intermolecular stretches and bends. Rotational linewidths are laser bandwidth limited suggesting a lower limit of approximately 250 ps for the lifetime of the ν1 level.